Much work is currently being done in the area of electronic communication networks.
In one specific area, that of telephone systems, much effort is now being made to convert traditional analog telephone communication systems to the so-called Integrated Services Digital Networks (or "ISDN") standard.
More specifically, in traditional telephone systems, analog-based equipment is used to convert voice data (at an originating source) into a continuously fluctuating signal which is transmitted over a wire to a remote location, where other analog-based equipment is used to convert the continuously fluctuating signal back into voice data for receipt by a receiving party. At one time, substantially all of the equipment in the telephone system constituted analog-based equipment. Later, particularly with the advent of electronic digital switches, it was found that substantial advantages could be obtained by making at least an intermediate portion of the system be digitally-based rather than analog-based. In addition, it has also been found that digitally-based signals (such as those originating in digitally-based computers) can be transmitted more efficiently with fully digital systems than with solely analog, or even hybrid analog/digital, systems. As a result, a new ISDN standard has been established in which all data flows through the network in purely digital form, it being the task of the systems's front-end equipment to convert any non-digital incoming data into purely digital signals before sending it out over the network.
A complex series of protocols governs how the various elements in an ISDN network operate and how they interact with one another.
More particularly, and looking now at FIG. 1, in an ISDN system, the aforementioned front-end equipment at the originating source is typically referred to as a terminal equipment (or "TE") device, and that portion of the network interfacing with the TE device is typically referred to as a network termination (or "NT") device. The interface between the TE device and the NT device is typically referred to as the "S" interface; the interface between the NT device and the remainder of the network is typically referred to as the "U" interface.
A TE device can be any piece of equipment which provides digital data to the network or takes digital data off the network. For example, a TE device might be a telephone, or it might be a computer, or it might be a fax machine. Regardless of the particular function of the TE device, in an ISDN system all TE devices must provide their data to the network (or receive their data from the network) according to ISDN standards.
By way of further explanation, in some cases the TE device may be a native ISDN device, in the sense that it has been preconfigured to output its data to the network (or receive its data from the network) according to the appropriate ISDN standards. In this case such a device may be referred to as a "TE1" device. Examples of a TE1 device might be an ISDN telephone, or an ISDN computer, or an ISDN fax machine. In other cases the TE device may consist of a non-ISDN device (i.e., a "TE2" device) in combination with a terminal adapter device (i.e., a "TA" device). In such a situation, the TA device sits between the TE2 device and the network and converts any data output by the TE2 device into the form required by the ISDN network (or converts any data received from the network into the form required by the TE2 device). The interface between the TE2 device and the TA device is typically referred to as the "R" interface. Examples of a TE2 device might be a fax machine or a modem. The aforementioned NT device comprises the network switch equipment which sits at the end of the ISDN network (typically at the telephone customer's premises) and interacts with the TE device.
By way of further explanation, the NT device could consist of just the network switch device itself (i.e., a "NT1" device), or it could consist of an NT1 device in combination with another device (i.e., an "NT2" device), wherein the NT2 device is interposed between the NT1 device and the TE device. In the case where the NT device consists of an NT1 device in combination with an NT2 device, the interface between the NT1 device and the NT2 device is typically referred to as the "T" interface.
Regardless of whether the NT device consists of simply an NT1 device or an NT1 device in combination with an NT2 device, the NT device always interfaces with the TE device at the S interface and always interfaces with the remainder of the network at the U interface.
The present invention is concerned solely with the S interface.
In addition to the foregoing, the ISDN standard requires that all communications flowing through the network subscribe to a multilayer communications model.
More specifically, and looking now at FIG. 2, all communications flowing through the ISDN network must subscribe to a 3 layer communications model, wherein Layer 1 is the "physical" layer, Layer 2 is the data link layer, Layer 3 is the network layer. It is to be appreciated that the aforementioned 3 layers of the ISDN network themselves comprise the lowest three layers of a broader 7 layer ISO communications model, wherein Layers 1-3 comprise the three layers of the ISDN standard, Layer 4 is the transport layer, Layer 5 is the session layer, Layer 6 is the presentation layer, and Layer 7 is the application layer.
The present invention is concerned solely with Layer 1, i.e., the so-called "physical" layer.
In a hardware sense, and looking now at FIG. 3, the TE device is connected to the NT device by means of RJ45 cabling.
More specifically, the RJ45 cabling consists of four pairs of twisted wires, i.e., wire Pair A, wire Pair B, wire Pair C, and wire Pair D, with Pair A being connected to Pins 1 and 2 of the RJ45 jack, Pair B being connected to Pins 3 and 6 of the RJ45 jack, Pair C being connected to Pins 4 and 5 of the RJ45 jack, and Pair D being connected to Pins 7 and 8 of the RJ45 jack. Currently, under the ISDN standard, Pair A (i.e., Pins 1 and 2) are not used, Pair B (i.e., Pins 3 and 6) are used for the transmission of data, Pair C (i.e., Pins 4 and 5) are used for the reception of data (and, optionally, to supply power to the TE device, if desired), and Pair D (i.e., Pins 7 and 8) are used for "phantom" power (i.e, to allow the ISDN network to supply power to the TE device, if desired).
It is to be appreciated that a typical TE device generally comprises at least one RJ45 jack to permit the TE device to be connected to an associated NT device, and a typical NT device generally comprises numerous RJ45 jacks to permit the NT device to be connected to multiple TE devices.
It is also to be appreciated that, in accordance with ISDN standards, the information being transmitted across the S interface consists of discrete bundles (or "frames") of digital data.
More specifically, and as seen FIG. 4, each frame of data crossing the "S" interface consists of 48 bits of digital information, transmitted at a nominal bit rate of 192 kbps (kilobits per second). Various portions of each frame relate to signaling information used to coordinate the interaction of the TE and NT devices on the ISDN network, while other portions of each frame carry the actual data being transmitted over the network.
Due to the nature of the ISDN network, it is imperative that (1) the network's RJ45 cabling be installed consistently with ISDN standards, (2) the TE and NT devices be coupled correctly to the RJ45 cabling, and (3) the TE and NT devices operate consistently with ISDN standards.
When a particular TE device is brought on-line in an ISDN network, a preliminary handshaking routine is conducted between that TE device and its associated NT device to ensure that all of the foregoing is in proper working condition and that the TE device is ready to access, or to be accessed by, the network.
More particularly, and as seen in FIG. 5, the TE and NT devices exchange a series of signals with one another, in interlocking fashion, as the devices make the necessary preliminary handshake. This is done in the following manner. The NT device first sends an INFO 0 signal to the TE device. When the TE device successfully receives this INFO 0 signal, it responds by sending an INFO 1 signal back to the NT device. When the NT device successfully receives this INFO 1 signal, it responds by sending an INFO 2 signal back to the TE device. When the TE device successfully receives this INFO 2 signal, it responds by sending an INFO 3 signal back to the NT device. When the NT device successfully receives this INFO 3 signal, it responds by sending an INFO 4 signal back to the TE device. If the TE and NT devices successfully pass through the foregoing handshaking procedure, the TE device is properly synchronized with the NT device and "line activation" has been achieved. The TE device may then access, or be accessed by, the network. In the event that the TE and NT devices are not able to successfully pass through the foregoing handshaking procedure, no activation takes place and the TE device is not able to access, or be accessed by, the network.